This invention relates to an antenna array having pairs of sandwiched radiating elements and a stripline transmission feed of signals to/from the elements. The antenna array is implemented as part of a layered printed circuit board like assembly.
Conventional self-complementary antennas, e.g. bowtie antennas, have been utilized for various purposes such as for the reception of broadcast UHF television signals. Although a single bowtie antenna can be utilized, an array of bowtie antennas is commonly utilized to increase gain, for example an antenna array having 4 active bowtie antenna elements all disposed in the same plane. A balun (balanced to unbalanced) transformer is normally used to couple the bowtie antenna elements to a transmission line to provide a match of the antenna impedance and the impedance of the feed line.
Another antenna design utilizes a patch antenna structure. For example, a patch antenna may utilize a conductive element spaced apart from a ground plane. A patch antenna may utilize a plurality of radiating elements to increase gain and/or achieve a desired radiation pattern.
The design and construction of a practical wideband antenna array having wide scan capabilities has proved to be challenging. Many antennas require the use of a balun as part of the feed mechanism in order to provide an impedance match of the radiating elements to the transmission mechanism. A balun has inherent signal loss and will likely have less than optimal signal transfer characteristics over a wide frequency range. For an antenna array utilizing a substantial number of radiating elements, a balun will likely be required to feed each of the radiating elements or group of elements. In addition to these difficulties related to having one or more baluns, such an antenna array is costly to manufacture. Where a dipole antenna is used, especially without the use of a balun, it is difficult to maintain symmetry of feed point.
A desirable characteristic for a wideband antenna array is the ability to select horizontal or vertical polarization without requiring physical movement of the antenna array. Many conventional antenna arrays have a single fixed polarization orientation requiring the physical rotation/movement of the antenna array to effectuate a change of polarization. This can be implemented but it is at the expense of additional structure required to control the physical rotation/orientation of the antenna array. Such an implementation carries with it additional cost and increased maintenance of the structure. There exists a need for a cost-effective practical wideband antenna array which minimizes at least some of these difficulties.